1. Field of the Invention
The present invention relates to a chemical vapor deposition method for making a semiconductor thin film, by which the uniformity of thin films allowed to deposit from vapor phase simultaneously onto a plurality of substrates is improved particularly between the substrates and inside the substrate.
2. Discussion of Background
Generally, in the chemical vapor deposition method for the thin film of semiconductor, as shown in FIG. 4, a gas introductory port (2) and a gas exhaust port (3) are provided at the upper portion and the lower portion of a vertical type cylindrical reaction tube (1), respectively, a plurality of semiconductor substrates (5) are fitted onto the side faces of carbon susceptor (4) in the shape of polygonal frustum provided coaxially in the reaction tube (1), and the source gases and the carrier gas are introduced from the gas introductory port (2) at the upper portion to be flowed downwards and ejected from the exhaust port (3) at the lower portion. In this way, the substrates (5) are heated to a predetermined temperature to allow the source gases near the substrates (5) to react through thermal decomposition and the thin films of semiconductor are allowed to deposit onto the substrates (5).
The substrates (5) are subjected to high-frequency heating by providing an RF coil (6) around the outer circumference of the reaction tube (1) and, in order to prevent the thermal decomposition of source gases except near the surface of the substrates (5), the reaction tube (1) is made of a double quartz wall forming a jacket (7) having a refrigerant inductory port (8) and a refrigerant exhaust port (9) and the refrigerant is flowed into this jacket (7) to cool the reaction tube (1). Moreover, in order to make the thickness of the deposited semiconductor thin film uniform by averaging the discrepancy in the geometrical symmetry between the susceptor (4) and the reaction tube (1) and the discrepancy in the geometrical symmetry of the exhaust port (3), a rotational axis (10) is provided to the susceptor (4) to allow the susceptor (4) to rotate at a constant number of rotations. Besides, in the diagram, the numeral (11) indicates a preparation chamber to exchange the substrates (5) having allowed the thin films of semiconductor to deposit, (12) indicates a gate valve, (13) indicates a hydrogen introductory port, and (14) indicates a frange of substrate loading.
In the conventional chemical vapor deposition method, although the variation in the thin films deposited may be improved considerably between the substrates by allowing the susceptor to rotate at a constant number of rotations, there is a shortcoming that the variation in the thin film in the direction perpendicular to the flow of gas is large in the substrate. FIGS. 5 (A) and (B) show the variations in the thickness of thin films deposited by the conventional chemical vapor deposition method described above in the direction perpendicular to the flow of gas, wherein (A) shows the case of clockwise rotation and (B) shows that of counter-clockwise rotation. It can be seen that the variations in the thickness of film are large in all cases. Moreover, this dispersion becomes more remarkable as the number of rotations of susceptor increases.